She was argumentative and combative to the point that she was fired from her job as an interior decorator. She grew distant. Ultimately, she did not know him.

She was his mother, Marilyn Robinson. Five months ago, she died of respiratory failure, but for nine years before that, she had fought a losing battle with Alzheimer`s disease.

In the end, her crippled brain could no longer tell her body to swallow and keep her breathing passages clear.

She was 51 when she was diagnosed with the degenerative brain disease that affects more than 2.5 million Americans.

On Friday, Marilyn Robinson`s son began his 4,700-mile journey, which he has named the ``Ride for Reason,`` at a Miami nursing home. By the time David Robinson rolls into Seattle 124 days later, he hopes to have raised $100,000 for the Alzheimer`s Disease and Related Disorders Association.

And he hopes to have exorcised some of his own ghosts.

``Since it hasn`t been that long since my mother died, I still have some internal work to do,`` said Robinson, 26, who still lives in Columbus, Ohio, where he grew up. He plans 24 stops at ADRDA affiliates from the Greater Miami chapter to the Puget Sound chapter.

Robinson is braced for retelling his mother`s story often, and he likes to start with how his mother was: ``Very artistic, she was a watercolor painter. She was very active in our church, very kind and gentle.``

Then he talks about what she became, twisted by Alzheimer`s.

``We first knew something was wrong, because she became so demanding and bossy, which was very unlike her.``

David`s father, research scientist Gerald Robinson, tried to care for his wife at home, but her behavior made their life impossible.

In 1983, Marilyn Robinson finally was placed in a nursing home.

Robinson, a marketing consultant, took a seven-month leave of absence to plan and complete his Ride for Reason. So did his traveling companions Allison Ploeger, a 27-year-old public relations specialist also from Columbus, and Mark Smith, 26, from Texas. Ploeger and Smith are driving the bright yellow support van that hauls the team`s camping gear, supplies and extra bicycles.

And David Robinson will ride against the prevailing spring winds. The more difficult east-to-west route was deliberately selected.

``People who must care for Alzheimer`s victims go through so much every day. I thought going against the wind was appropriate,`` he said.

More information on the Ride for Reason is available by writing to ADRDA, Columbus Area Chapter, 2323 W. Fifth Ave., Suite 2100, Columbus, Ohio, 43204. The telephone number is (614) 481-8834.